Thank you for all these comments on the Notebook. Michael is absolutely right - like everyone else, I always assume it's either manned or unmanned. Perhaps combined missions are an answer, but having humans on board would inevitably be a limiting factor in terms of where you could send missions. You still need to get those astronauts back home safely, which means you can't send them too far away.

I'm taking a summer break now but, when I return, I'll try to make time to respond each week to the comments I receive. I do read them and am genuinely grateful to all the readers who take time out to offer such insightful, thought-provoking views.

anjana ahuja, london, uk

Dear Ms Ahuja,

The headline of your article depicts only two options: robots or humans. You could add a third option: both. Given a choice between robots, humans or both, I think that most people would vote for option 3.

Michael Huang, Melbourne, Australia

Bingo,Anjana. Your science book theory somewhere remotely connects with another belief, better known in the field of parapsychology as "psychic soliloquism" Sounds a bit gibberish, like a jargon or some gobbledegook, but it relates to a very important inherent trait among us, as human beings. What makes humn beings different from other animals. We can think, or rather think rationally .
But to think rationally, one aught to debate with oneself....much like a one-on-one tete'-a-tete' . Before a thought originates in our mind, we unknowingly or unconsciously talk to our "other self", say you conscience being, or soul or whachumacallit.
It is like a robotic process, between our brain lobes, and the hypothalamus, or the seat of conscience.At times when the two thought processes differ, we run into a mental " tug-of-war",and when they sync or gel up, it improves our self belief.
More intellectual a person is, there are more chances of commiting heinous acts like murder, terrorism etc.

sandy, New Delhi, India

Helen Sharman's reaction is, perhaps, understandable. Human acheivement is generally measured by the reactions of others. As we have become increasingly globalised the number of people who can give a positive reaction to a specific acheivement has, you'll forgive the pun, sky-rocketed. As such it is easy for that praise (or disapprobation) to be overwhelming, especially when focused on a non-repeatable event of finite duration. Her desire to "move on" is understandable, is possibly futile.
Colin Pillinger, for whom I have nothing but respect and fondness, was not in the same position. His career could continue, he could strive for other peaks that might even surpass the Beagle project.
I have never aspired to be an astronaut, partly because the sense that my life had reached its crown so early would devastate me. The fate of astronauts in the real world may not be the same as in William Gibson's short story Hinterland, but perhaps it's not too far different.

Tom Foster, London, UK

Space-faring expertise with robots doesn't necessarily translate into space-faring expertise with humans. Its pointless to know what's on Mars, if the means to know what's there don't get us any closer to being there.

Alexander V. Grigorov, Varna, Bulgaria